August 2012
Intermediate to advanced
624 pages
17h 11m
Polish
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6.4. Sprawdzanie więcej niż jednego warunku
Problem
Czy w przypadku konieczności zweryfikowania więcej niż jednej właściwości pliku trzeba zagnieżdżać poszczególne instrukcje if?
Rozwiązanie
Dzięki operatorom sumy logicznej OR (-o) i iloczynu logicznego AND (-a) można połączyć kilka warunków w jedno wyrażenie. Oto przykład:
if [ -r $PLIK –a –w $PLIK ]
Instrukcja ta sprawdza, czy plik można odczytywać i zapisywać.
Analiza
Wszystkie testy właściwości plików zawierają niejawny test na obecność pliku. Nie ma więc potrzeby sprawdzania, czy plik istnieje i czy można odczytywać z niego dane. Nie można odczytywać danych, jeśli plik nie istnieje.
Operatory łączenia testów (-a dla iloczynu logicznego i –o dla sumy logicznej) mogą być stosowane w dowolnych wyrażeniach ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.